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Commit f7b8a47d authored by Kirill Tkhai's avatar Kirill Tkhai Committed by Ingo Molnar
Browse files

sched: Remove lockdep check in sched_move_task() 



sched_move_task() is the only interface to change sched_task_group:
cpu_cgrp_subsys methods and autogroup_move_group() use it.

Everything is synchronized by task_rq_lock(), so cpu_cgroup_attach()
is ordered with other users of sched_move_task(). This means we do no
need RCU here: if we've dereferenced a tg here, the .attach method
hasn't been called for it yet.

Thus, we should pass "true" to task_css_check() to silence lockdep
warnings.

Fixes: eeb61e53 ("sched: Fix race between task_group and sched_task_group")
Reported-by: default avatarOleg Nesterov <oleg@redhat.com>
Reported-by: default avatarFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: default avatarKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1414473874.8574.2.camel@tkhai


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 980d0d51

kernel/sched/core.c

+6 −2
Original line number Diff line number Diff line
@@ -7444,8 +7444,12 @@ void sched_move_task(struct task_struct *tsk) 
	if (unlikely(running))

		put_prev_task(rq, tsk);



	tg = container_of(task_css_check(tsk, cpu_cgrp_id,

				lockdep_is_held(&tsk->sighand->siglock)),

	/*

	 * All callers are synchronized by task_rq_lock(); we do not use RCU

	 * which is pointless here. Thus, we pass "true" to task_css_check()

	 * to prevent lockdep warnings.

	 */

	tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),

			  struct task_group, css);

	tg = autogroup_task_group(tsk, tg);

	tsk->sched_task_group = tg;